Heads Up: Removed LIBC_BUILTINS

For any Linux or GNU/kFreeBSD users who may have previously used
LIBC_BUILTINS in their mk.conf, it no longer exists, and has been
replaced by the new _OPSYS_PREFER mechanism.
It was previously introduced with this change:
Author: sbd <sbd>
Date: Mon Oct 31 23:22:59 2011 +0000
Add LIBC_BUILTINS platform definition to Linux.
Designed to be used in mk.conf like so:
PREFER_PKGSRC= yes
PREFER_NATIVE= ${LIBC_BUILTINS}
With the recent change, the PREFER_NATIVE line is no longer necessary.
Thanks,
--
Jonathan Perkin - Joyent, Inc. - www.joyent.com